The telecommunication and data communication networks are today built as separate overlay networks. The result is that transport and switching for data belonging to different applications are performed in separate equipment, e.g. Frame Relay switches and networks for one type of LAN-to-LAN interconnect traffic and PSTN/ISDN switches and networks for voice traffic. With the introduction of ATM, a common switching network is possible for all these services. This also facilitates a common access for all types of traffic, e.g. data, voice and video, thus reducing the amount of network equipment.
However, for voice traffic, a number of supplementary services have been developed for both the end-user and the service provider. Such services can be screening services for closed user groups, call distribution services, flexible billing mechanisms, various access methods, etc. This multitude of services is implemented in today's narrowband equipment supporting PSTN and ISDN.
When providing a common access point, and transport and switching function by using ATM for both voice, data and video, a new network has to be built having these switching capabilities.
A requirement is that a new network using ATM as the common switching method has to provide all existing services supported by the narrowband voice networks in operation today. Neither the end-user nor the service provider can be requested to drastically lower the service content by the introduction of ATM.
The existing solution to meet this requirement is to use ATM as a pure transport mechanism. This is done by trunking either point-to-point between narrowband equipment such as PBXs or access devices, or by trunking towards a narrowband switch, see-ATM Forum/95-0446R9, Baseline Text for Voice and Telephony Over ATM—ATM Trunking For Narrowband Services, ATM Forum, August, 1996.
Thus, for example in FIG. 1, two different narrowband equipments 101 and 103 are shown, which communicate, at least partly, over an ATM network 105 to which a narrowband switch 107 also is connected. The narrowband switch can for example be an AXE switch manufactured by the company Ericsson. In the figure, the interfaces A are existing narrowband trunks comprising voice circuits and signalling capabilities. The line I illustrates a point-to-point trunking of the complete narrowband trunk between the two narrowband equipments, and connections II provide the capabilities of providing telephony services with ATM transport, but no switching.
The problems associated with the existing solutions are:
i) The trunking for point-to-point trunks (I) generally requires a meshed network, i.e. in order to interconnect N narrowband equipments/network access points N(N-1)/2 trunks through the ATM network are required.
ii) Trunking towards a narrowband switch still requires that all voice traffic is STM (Synchronous Transfer Mode) switched in the narrowband switch, and the ATM switching capabilities are not used. An extra STM-ATM transition also introduces delays that must be coped with, or affected voice quality will have to be accepted.iii) There will be a waste of resources in the ATM network, the capabilities of which are not fully used.
A description of how this is proposed to be implemented in the network is provided by ATM Forum in their Voice and Telephony Over ATM (VTOA) group.
Also the international patent application WO/97 09807, describes a system for providing virtual connections through an interworking multiplexer on a call by call basis. The system uses established ATM connections.